If one cannot withdraw the required German units then all replacements points are lost - does this also apply to the Withdrawal from France extra replacement point which is not affected by the approval track?

I fear so. Rule 17.2.1 (misnumbered 17.3.1) says exactly that with ALL in capitals. Rule 19.1.3 3rd bullet point has an exception from dismissal but not from inability to withdraw units.

The British have easier terms, paying the number of replacement points that would buy back the dead. Of course the Brits only lose 2 infantry divisions (though one's elite) whilst OB West loses 20 divisions, 6 of them panzer and 3 panzer-grenadier.